454 MANUAL OF HISTOLOGY. 



tive tissue representing the former lactiferous canals. The 

 terminal portions of these larger duct-remnants are sometimes 

 connected with minute channels, the latter being the remnants 

 of collapsed smaller ducts. In some measure we find a com- 

 pensatory production of fat, which partly replaces the faded 

 acini. The breasts of old women, therefore, consist of fibrous 

 tissue, with a large proportion of elastic elements, fat-cells, and 

 the remnants of the ducts. It may be remarked that the latter 

 frequently show cystic dilatations, the cavities being filled with 

 a dirty, slimy fluid. The blood and lymph-vessels, but especi- 

 ally the latter, participate in the general atrophy of the tissues. 



This succinct account concerning the histogenesis of the 

 mammary gland, does not, as already intimated, represent the 

 unchallenged opinion on its first development. For Creighton, 

 in the remarkable work already cited, radically opposes the 

 view that the mamma takes its origin from the epiblast. He 

 believes, on the contrary, that it starts from the mesoblast, or 

 connective-tissue layer of the embryo, and not the upper epi- 

 thelial layer or epiblast. According to him, moreover, and his 

 conclusions are based on developmental studies, chiefly of the 

 guinea-pig's gland, the process may be justly described as a 

 centripetal one, whereas the current view represents this gland- 

 develpoment as essentially centrifugal. We have already ex- 

 pressed our adherence to the current view, attributing this 

 growth to extension from a central point. Nevertheless, it 

 seems proper to briefly give the conclusions of Creighton, es- 

 pecially since they appear to be singularly corroborative of the 

 account given by Goodsir of this process, as early as 1842, an 

 account which has apparently remained almost unnoticed by 

 workers in this branch of scientific medicine. 

 , Creighton then concludes his inquiry as follows : 



" 1. The mammary acini of the guinea-pig develop at many 

 separate points in a matrix -tissue. The embryo cells from 

 which they develop are of the same kind that give origin to 

 the surrounding fat-tissue. The process of development of the 

 mammary acini is, step-for-step, the same as that of the fat- 

 lobules." 



" 2. The ducts of the mamma develop from the same matrix- 

 tissue, by direct aggregation of the embryonic-cells, along 

 predetermined lines. The ducts develop, in the individual 

 guinea-pig, before the acini, whereas, in the phylogenetic sue- 



